In the case of providing connection between two points with a conductive wire in the manufacturing of a semiconductor device (integrated circuit device), a wire bonding apparatus has been used. For example, when a semiconductor device is manufactured by using a lead frame having a tab and a plurality of leads extending toward the tab, a semiconductor element (semiconductor chip) is fixed to the principal surface of the tab and then the electrodes of the semiconductor chip are connected to the leads with conductive wires.
In wire bonding, a technology which applies heat and a technology which applies heat and ultrasonic vibration have been known to achieve a satisfactory bonding strength when connection is provided by physically squashing the wires. A system for the former technology is termed a thermocompression wire bonding apparatus and a system for the latter technology is termed a thermosonic wire bonding apparatus.
Thermosonic wire bonding apparatus are disclosed in, e.g., Japanese Unexamined Patent Publications No. Hei 7 (1995)-147297 and No. 2000-332050. Each of these documents discloses a technology which sprays a cooled air to a horn to suppress a reduction in bonding accuracy resulting from the heat-induced expansion of the horn. The former one of the documents discloses a technology which sprays a cooled air to a portion including the body tube of a sensing camera and a camera support arm for supporting the sensing camera.
As for the technology for heating a wire, it is disclosed in, e.g., Japanese Unexamined Patent Publication No. Hei 6 (1994)-104319. In one of the wire heating methods disclosed in the document, a wire bonding tool (capillary) is constructed such that a laser absorption film is provided on the wire compression surface of the tool, while a laser reflection film is provided on the surface of the tool except for the wire compression surface and a surface on which a laser beam is incident, and a laser beam incident upon the tool is focused on the absorption film to apply heat, which is conducted from the absorption film directly to the wire. However, the bonding tool is complicated in structure and high in manufacturing cost.
On the other hand, an organic resin wiring substrate such as an epoxy resin substrate containing glass has been used as a device substrate which is a component of a semiconductor device. As for the organic resin wiring substrate, it is described at pages 16-30 of the October 2001 issue of Electronic Materials, published by Kogyochosakai Publishing Co., Ltd.
Each of a thermocompression wire bonding apparatus and a thermosonic wire bonding apparatus performs wire bonding by placing a lead frame and a wiring substrate on a wire bonding stage in a heated state. If a copper plate having a large thermal expansion coefficient is used as the lead frame, the lead frame is prone to thermal deformation and therefore high-accuracy wire bonding could not be performed.
In an organic resin wiring substrate using an organic resin in the base material or surface portion thereof also, a line on the surface thereof elongates due to the considerable thermal expansion of the organic resin and therefore high-accuracy wire bonding could not be performed.
Against the deformation resulting from the thermal expansion of the wiring substrate or the lead frame, measures can be taken in which the position of a line or lead as a wire bonding target is recognized prior to a wire bonding step, and a bonding position is corrected. However, once a holder for holding a camera or a horn for holding a capillary for performing wire bonding is expanded by radiated heat resulting from the heating of the wire bonding stage and displaced, the problem of an inevitable reduction in wire bonding accuracy occurs unless a mechanism for correcting the displacement thereof is provided.
It has also been proved that the use of an organic resin wiring substrate generates an organic gas and reduces wire bondability, as has been described in the specification of the invention already applied for patent by the present inventors.
That is, an insulating layer is formed on the surface of a wiring substrate (organic resin wiring substrate) such as an epoxy substrate containing glass used for a semiconductor device or in the inside thereof. For example, there is a wiring substrate having an insulating film such as a solder resist film for insulating surface lines which is formed on the surface thereof and also an insulating layer made of an epoxy material serving as a base material which is disposed in the inside of the wiring substrate. The insulating layer of such a wiring substrate is formed mainly from an organic resin.
In a wire bonding step, the wiring substrate is heated to a high temperature so that an organic gas is generated from the insulating layer. The organic gas is cooled by each of the parts of the apparatus arranged around the wiring substrate and deposited as an organic substance. There is a risk that, if the organic substance is deposited on each of the parts of the wire bonding apparatus, the apparatus might not operate smoothly. If an organic substance adheres to a cylindrical capillary which is holding a wire, the wire is not smoothly fed out of the capillary any more and excellent wire bonding cannot be performed.
An object of the present invention is to provide a method for manufacturing a semiconductor device which provides an excellent wire bonding property.
The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.